Fire stopping is the work of closing every hole through a fire resisting wall or floor so the compartment actually holds. It is the least visible trade on a building and the one most often found defective, because the holes are made by other trades, at different times, and nobody owns the gap between them.
Why it exists
A compartment wall rated for an hour is rated for an hour with no holes in it. Every pipe, cable, duct and fixing that passes through is a route for fire and smoke, and hot gases will find a small opening long before flame reaches the wall. Fire stopping restores the rating at each of those openings, using a system tested for that opening in that construction.
The materials and where each belongs
Fire rated mastic and sealant for small linear gaps and movement joints. Compound, a pourable or trowellable material, for floor openings around cable trays and small services. Coated batt, mineral wool board with an ablative coating, for larger service openings in walls. Pillows for openings where services change often. Collars and wraps for plastic pipes. Fire rated foam only where a tested system uses it, never ordinary expanding foam.
Pipes and floors are the hard cases
A plastic pipe through a wall burns away and leaves an open hole, so it needs a collar or wrap that crushes it closed. A metal pipe conducts heat and can ignite material on the far side, so the detail is different again. Floors are harder than walls because compound has to be contained while it sets and because the opening is usually full of cables somebody will add to next month.
The evidence is the deliverable
A fire stopping installation should leave behind a record of every penetration: where it is, what services pass through, which system was used, who installed it and when, usually with a photograph and a label at the penetration. Without that, the next person has no way to know whether a seal is a tested system or a tube of something. Third party certification for fire stopping installers exists for the same reason.
Questions people ask about fire stopping compound
What is fire stopping?
Sealing the openings through fire resisting walls and floors, using systems tested for that opening in that construction, so the compartment performs for its rated period.
Can I use expanding foam for fire stopping?
Only a fire rated foam used within a tested system. Standard expanding foam is not fire resisting and is one of the most common hidden defects in British buildings.
What record should fire stopping leave?
A schedule of every penetration with its location, the services through it, the system used, the installer and the date, usually with photographs and a label at the penetration itself.